论塔里木盆地“东河砂岩”的地质时代

THE AGE OF THE DONGHE SANDSTONE IN THE TARIM BASIN

系统总结了关于近年来塔里木盆地重要储油层——“东河砂岩”年代研究所取得的主要进展 ,包括 1)“东河砂岩”中发现晚泥盆世孢子和胴甲鱼化石 ; 2 )含砾砂岩段发现晚泥盆世盾皮鱼化石 ; 3)下泥岩段下部发现晚泥盆世孢子 ; 4 )下泥岩段上部和生屑灰岩段分别发现石炭纪初期第一、二孢子组合带 ; 5 )生屑灰岩段发现石炭纪初期的牙形刺 ; 6 )化学 -生物地层学研究结果指示 ,泥盆系 -石炭系界线应在“东河砂岩”顶面之上。据此 ,“东河砂岩”的时代应为泥盆纪。

The age of the Donghe Sandstone, one of the main oil bearing strata in the Tarim Basin overlaid by the Bachu Formation (including Conglomerate Sandstone, Lower Mudstone and Bioclastic Limestone Members), is intensely concerned by geologists both at home and abroad. During the beginning years after this suit of sandstone was first revealed in the bore DH 1 in the northern part of the basin in 1990, geologists had regarded it as the Lower Carboniferous for the absence of reliable fossils recovered therein. However, in the past 5 years, more and more palaeontological evidence has emerged showing that the age of the Donghe Sandstone seems to be Late Devonian. Synthesizing all the palaeontological data related to the Donghe Sandstone we have obtained, a) the spore assemblage recognized from the Donghe Sandstone of the bore Cao 2, is Late Devonian age; b) the fish fossils assigned to the Antiarchian obtained from the Donghe Sandstone of the bore Cao 2 suggest a Late Devonian age; c) the earliest Carboniferous spore assemblage zones are recognized from the upper part of the Lower Mudstone Member and the Bioclastic Member of the Bachu Formation of the bore TZ401; d) the spores from the lower part of the Lower Mudstone Member of the bore Ma 5 indicate an age of Late Devonian; e) the fish fossils assigned to the Placoderm from the Conglomerate Sandstone Member of the bore TZ45 is regarded to be Late Devonian in age; f) the conodont assemblage from the Bioclastic Member shows transitional characters of Devonian Carboniferous boundary; g) correlation between the Tarim and South China by chemo biostratigraphy reveals that the Devonian Carboniferous boundary may be defined at a level 51.5m above the top of the Donghe Sandstone.